Fiber reinforced plastic (FRP) composites are finding increasing usage as a replacement for metal and other structural materials especially with automotive and aerospace industries due to their high strength and low weight. However, every 1000 mph increase in speed results in an increase in the skin temperature of the airframe by about 100 degrees F. Epoxy resins have been the matrix resins usually used in FRP composites. However, these resins exhibit very poor strength in humid environments and at elevated temperatures, i.e. they exhibit a very low wet Tg (glass transition temperature).
Bis-imide resins exhibit good humidity resistance and are capable of use as matrix resins in humid, high temperature environments. However, the available bis-imide resin systems have exhibited long gel and cure times even at high curing temperature up to 475 degrees F. High modulus graphite composites cured with these resins have exhibited severe microcracking after cure due to shrinkage caused by gelation at high temperatures.
Other suitable requirements of a matrix resin are that the neat resin should have good tack and be capable of being cured in low pressure autoclaves (about 100 psi) in a few hours at less than 350 degrees F. in order to be compatible with typical industrial usage and equipment as practiced with epoxy resin composites. The neat resin should also exhibit good elongation and strength and have low shrinkage when cured. The cured resin should also have a high Tg and exhibit low shrinkage when cured and have good latency, i.e. long pot life at temperatures below 100 degrees F.